This server could not prove that it is www.cacert.org; its security
certificate is not trusted by your computer's operating system. This
may be caused by a misconfiguration or an attacker intercepting your
connection.

So in this case, we are getting "Your connection is not private" error,
because the service is using a certificate signed by an unknown root CA.
But you can still continue to use www.cacert.org, as long as you
trust the group who runs the website. No other people can see
your communication data, since the data is still encrypted.

See the picture below shows you the "Your connection is not private" error in Google Chrome: